Article history: Received 9 August 2008 Received in revised form 30 November 2008 Accepted 19 December 2008

for his invaluable guidance, support, time, and understanding (and tolerance) this past year. Lastly, I thank my parents for their perseverance in dealing with me for the last 24 years. It really is quite a feat.

CAPTCHAs are known as Captcha which stands for Completely Automated Public Turing test to tell Computer and Human Apart. used prevent automated scripts from harvesting email addresses publicly accessible forms on the internet submitting them spammers. mostly utilised because computers have a difficult time deciphering text concealed behind distorted visuals, but humans an easier information hid...

Online password guessing attacks are a serious threat to the integrity of online accounts. A common defense is ratelimiting, either by slowing down or blocking connections, or by requiring CAPTCHAs to be solved. Either of these options has serious drawbacks, facilitating denial of service attacks, being circumventable by proxies and CAPTCHA solving services, and offering bad usability to the le...

Providing security for webservers against unwanted and automated registrations has become a big concern. To prevent these kinds of false registrations many websites use CAPTCHAs. Among all kinds of CAPTCHAs OCR-Based or visual CAPTCHAs are very common. Actually visual CAPTCHA is an image containing a sequence of characters. So far most of visual CAPTCHAs, in order to resist against OCR programs...

CAPTCHA is a simple test that is designed to be easily generated by computers and easily recognized by humams, but difficult for computers to solve. It is now almost a standard security technology. The most widely deployed CAPTCHAs are text-based schemes, but to CAPTCHAs, segmenting the connected and distored characters is still an unsolving problem. In this paper, we proposed a Community Divid...

Recently proposed voter-verifiable protocols provide encrypted paper receipts to voters, who may later check that these receipts are in the electronic ballot box. This paper describes an enhancement that allows the voter to electronically transmit, from the polling booth, her encrypted receipt to an external verifier, who may perform the check on her behalf. It uses a CAPTCHA-like primitive – w...

Phishing is an attempt to commit fraud via social engineering. The impact is the breach of information security through the compromise of confidential data. Customers can access their banking accounts from anywhere in the world using their login ID and password. However, the use of password does not provide adequate protection against Internet fraud such as phishing. Phishing exploits this vuln...

A CAPTCHA is a program that generates challenges that are easy to solve for humans but difficult to solve for computers. The most common CAPTCHAs today are text-based ones where a short word is embedded in a cluttered image. In this paper, we survey the state-of-the-art of currently deployed CAPTCHAs, especially of some popular German sites. Surprisingly, despite their importance and the larges...